Internet of Things refers to a network of interconnection between people and things or between one thing and another by deploying various devices capable of, to some extent, perception, computation, execution and communication to obtain information of the physical world, and by means of information transmission, coordination and processing over the network. The Internet of Things may be applied to various aspects such as smart grid, intelligent agriculture, intelligent transportation, and environment check. Machine to machine (M2M) communication is a technology and a standardization concept that are proposed by the standardization organization-3rd Generation Partnership Project (3GPP) to research how to use a mobile communications network to carry applications of the Internet of Things, and a special project team is founded to research enhancement or optimization that needs to be performed on the mobile communications network due to introduction of machine type communication (MTC) devices.
Currently, in the 3GPP Long Term Evolution (LTE) project, a coverage enhancement research subject for the special application scenario of the MTC is proposed: providing coverage enhancement support for an MTC device that has a relatively great path loss (Pathloss, PL for short) when the MTC device is located in a basement or the like, so that the device can access the network to obtain a service. Signal repetition is one of methods for implementing coverage enhancement. Different MTC devices are located in different environments, and require different extents of coverage enhancement. Using signal repetition as an example, different MTC devices require different quantities of times of signal repetition.
According to the existing 3GPP protocols, a power of transmitting a random access preamble sequence in a random access process is determined according to the following formula:PPRACH=min{PCMAX,c(i),PREAMBLE_RECEIVED_TARGET_POWER+PLc},
where PCMAX,c(i) is a maximum transmit power of a terminal, PLc is a path loss of the terminal, PREAMBLE_RECEIVED_TARGET_POWER is a target received power of a base station, and PREAMBLE_RECEIVED_TARGET_POWER=preambleInitialReceivedTargetPower+DELTA_PREAMBLE+(PREAMBLE_TRANSMISSION_COUNTER−1)*powerRampingStep, where preambleInitialReceivedTargerPower is an initial target received power of the base station, DELTA_PREAMBLE is an offset (as shown in Table 1) corresponding to a format (format) of the preamble sequence, PREAMBLE_TRANSMISSON_COUNTER is a quantity of attempts to transmit the preamble sequence by the terminal, and powerRampingStep is a power ramping step in each attempt to transmit the preamble sequence by the terminal.
TABLE 1DELTA_PREAMBLE value tableRandom access preamblesequence formatDELTA_PREAMBLE value(Preamble Format)(DELTA_PREAMBLE value)0  0 dB1  0 dB2−3 dB3−3 dB4  8 dB
It can be learned from the foregoing formula that the transmit power of transmitting the preamble sequence by the terminal fully compensates for the path loss. That is, in an ideal case, the terminal transmits the preamble sequence at PREAMBLE_RECEIVED_TARGET+PLc. After undergoing the channel loss PLc, the sequence arrives at the base station at the power of PREAMBLE_RECEIVED_TARGET_POWER. Without power ramping, the sequence arrives at the base station at the power of preambleInitialReceivedTargetPower.
However, in a coverage enhancement scenario, because the path loss PLc undergone by a signal is relatively great, PREAMBLE_RECEIVED_TARGET_POWER+PLc is far greater than the maximum transmit power PCMAX,c(i) of the terminal. Therefore, the following case may occur: A receiving requirement of the base station cannot be met even if the terminal transmits the preamble sequence at the maximum transmit power. In this case, coverage enhancement needs to be performed on the preamble sequence, for example, by transmitting the preamble sequence repeatedly. How to determine the power of transmitting the preamble sequence in the coverage enhancement scenario becomes an urgent problem to be resolved.
In summary, currently there is no solution to determining a power of transmitting a preamble sequence in a random access process in a coverage enhancement scenario.